Tetrafluoroethylene (TFE) fine powder resins are non-melt-fabricable and are commonly processed by paste extrusion wherein the powder is mixed with a lubricant and is then discharged through a paste extruder to obtain films, tubes, tapes, protective coating on wire and the like.
Such paste extruded films, tubes and tapes can be rapidly stretched in unsintered form to form a strong material that is porous to water vapor but not to liquid water. Such a material is useful in providing "breathable" fabric material for garments, tenting, separatory membranes and the like. Many resins useful in making such paste extruded stretched films exhibit a sensitivity to lubricant loading levels and to stretch rates that necessitate careful control over the loading level used in order to ensure a good stretched product.
It is desirable to improve on these known resins by providing improved TFE fine powder resins that are not as sensitive to lubricant loading levels and which have improved stretchability. This invention is directed to preparation of such resins by using an initiator system not herefore used for this purpose.